1. Field of the Invention
This invention relates to using multiple fluids and energy to enhance recovery of viscous carbonaceous materials from geological resources.
2. Description of Related Art
Global demand for petroleum products continues to increase led by strong growth in China, India and the USA. However, discovery of conventional oil reserves has been declining since the mid 1960s. This is causing a strong growing demand for the recovery and conversion of heavy oil, bitumen from oil sands, kerogen from oil shale, and residual higher viscosity oil contained within conventional reservoirs, etc., (herein collectively termed, “heavy hydrocarbons”). Such alternative hydrocarbon resources have been more difficult, complex and expensive to recover and process than conventional petroleum resources.
Large deposits of oil sands are found in the Canadian province of Alberta and in the Orinoco region of Venezuela. Each reports total reserves in excess of one trillion barrels of oil equivalent (TBOE). Shallow minable, bitumen deposits are under heavy development, especially in Alberta. However, most bitumen in place is not economically recoverable using conventional surface extraction techniques.
The “energy returned on energy invested” (EROEI) strongly influences profitability and has been higher then 30:1 for conventional petroleum. However, the energy used to extract heavy hydrocarbons (especially oil shale) using conventional techniques may exceed the energy recovered (i.e. EROEI <1.0). Increasing rates of depletion and the maturity of conventional oil fields is generating strong demand to improve the EROEI for heavy hydrocarbons. This has led to several technological solutions to improve extraction efficiency and EROEI for these heavy hydrocarbon reserves.
For example, the Steam Assisted Gravity Drainage process (hereinafter SAGD) to extract bitumen from subsurface oil sands, was taught by Butler in U.S. Pat. No. 4,344,485, and by Nasr et al. in U.S. Pat. No. 6,230,814. Similarly, the Steam Assisted Gas Push (hereinafter SAGP) technique described in U.S. Pat. No. 5,407,009, and U.S. Pat. No. 5,607,016, both to Butler, et al., is a related technique. These have been described as recovering 40% to 50% of the bitumen in place.
The SAGD process injects steam into underground bitumen formations through horizontally drilled wells. The high enthalpy steam heats the bitumen, reducing its viscosity sufficiently to pump a portion of it out of geological formations using relevant art pump technologies, e.g., through a second parallel extraction or production well typically drilled about 5 m (17 ft) below the first injection well.
Carbon dioxide (CO2) has been used to increase the extraction rate of bitumen and other heavy hydrocarbons as well as other carbonaceous materials such as carbon tetrachloride. The extraction rate is defined as the rate at which the target material is being removed or delivered in either volume or mass terms. Deo, et al., Industrial Eng. Chem. Res., Vol. 30, No. 3, 1991, detailed the specific solubility of CO2 in various bitumens versus temperature and pressure. They reported decreases in viscosity with increasing solvation by CO2, e.g., in Athabasca (Alberta) & Tar Sand Triangle (Utah) bitumens and other similar heavy hydrocarbons.
Other patents, e.g., U.S. Pat. No. 4,217,956 to Goss, et al., and U.S. Pat. No. 4,565,249 to Pebdani, et al., detail other variations of the increase in bitumen or other heavy hydrocarbon extraction using CO2. In U.S. Pat. No. 4,565,249, the increase in bitumen or heavy oil extraction rate from oil sands increased by 36% by addition of 200 standard cubic feet (SCF) of CO2 per barrel of steam (1.6 vol % of CO2 in H2O) as compared to the case of pure steam extraction. The increase in extraction rate reaches a “plateau” with increasing CO2. In U.S. Pat. No. 4,217,956, bitumen recovery rates are at least doubled by the injection of CO2. The CO2 concentration used for those results was 750 SCF per barrel of steam (˜6.0 vol % of CO2 in H2O) at an ambient pressure of 300 pounds per square inch (psi) or 20.4 atmospheres (atm).
In U.S. Pat. No. 5,056,596 to McKay, et al., CO2 was dissolved in water at an alkaline pH (e.g., above 10.5) to enhance bitumen recovery rates. The CO2 is more soluble in alkaline solutions. However CO2 is often difficult to obtain near heavy hydrocarbon resources. Long expensive pipelines are typically used to deliver CO2.
The significant decrease in the viscosity of bitumen both with increasing solvation by CO2 and at increasing temperatures are important factors that underly the improvement in heavy hydrocarbon extraction efficiency with CO2. One objective of this invention is efficiently generate CO2 and enhance the extraction rate of heavy hydrocarbons.
Natural gas is a commonly used to heat heavy hydrocarbons and for power requirements in Western Canada's oil fields and oil sand processing plants because it is currently in relatively abundant supply in those locations. However, natural gas would be much better spent for premium applications requiring very low emissions. A catalytic desulfurization process or “Claus Process”, e.g. as described in U.S. Pat. No. 4,388,288 to Dupin, is currently used to remove the sulfur (usually found there in the form of hydrogen sulfide, H2S) from natural gas.
Heavy hydrocarbons including bitumen are similarly desulfurized during refining to synthetic crude oil. The market for elemental sulfur is currently saturated. Millions of tons of sulfur are currently stockpiled in the open air in Western Canada. A process to utilize some of this sulfur and other local raw materials for increasing the efficiency of heavy hydrocarbon extraction is therefore desired.
Other techniques have been utilized to add energy to the fluids used in the recovery of hydrocarbons from buried formations. For example, radio-frequency, (hereinafter, “RF”, including microwave) heating of the hydrocarbons in place are taught by Supernaw, et al. in U.S. Pat. No. 5,109,927, and by Kinzer in U.S. Pat. No. 7,115,847.
Other objectives are to increase the amount of bitumen recoverable, and to access deeper formations in an energy efficient manner. In addition, the energy costs of hydrocarbon extraction processes are a key area for potential improvement.
With respect to improving efficiency of energy production and costs, water has been used to control the combustion temperature and pollutant emissions in gas turbines for power production and other purposes (e.g., clean water production) as described in VAST (Valued Added Steam Technology) U.S. Pat. No. 3,651,461 to Ginter, U.S. Pat. No. 5,743,080 to Ginter, U.S. Pat. No. 5,617,719 to Ginter, U.S. Pat. No. 6,289,666 to Ginter, pending U.S. patent application Ser. No. 10/763,047 by Hagen, et al., and U.S. patent application Ser. No. 10/763,057 by Hagen, et al., herein incorporated by reference. Other references have proposed adding liquid water into the combustor to reduce nitrogen oxide (NOx) emissions but with corresponding increases in carbon monoxide (hereinafter, CO) emissions.
More careful control of adding liquid water (and/or steam) may simultaneously reduce both the CO and NOx emissions as described in the above-mentioned VAST cycle references. NOx is formed at high temperatures and CO is often formed when there is insufficient time for equilibration of the reaction products of a combustion reaction or when burning a fuel rich mixture. Conventional turbines using the “Simple cycle” or “Brayton Cycle” typically produces high lateral and axial temperature differentials which may lead to NOx formation at peak and high temperature locations regions in the combustor. Lateral temperature differentials (e.g., centerline to wall of outlet) as high as 500° C. are not uncommon at the outlet of such combustors.
VAST combustors may reduce these differentials to less than 100° C. This reduces peak temperatures with major reductions in NOx and CO formation, with more efficient operation. Well head crude combustion has been demonstrated in a VAST thermogenerator. VAST wet cycles recover exhaust heat to steam and hot water, resulting in large improvements in thermal efficiency and power density of gas turbines.
Consequently, an objective of the present invention is the use of VAST wet cycle combustion to produce combustion gases and heat for the efficient extraction or production of heavy hydrocarbons, and more particularly the use of alternative fuels, and improvements in hydrocarbon extraction efficiency by altering the fuel mix and combustion by-product composition.
Steam raised in boilers has been used or proposed to heat and recovery bitumen, kerogen, heavy oil, shale oil, residual oil, and other hydrocarbons from geological resources, alternately termed heavy hydrocarbons, HeavyHCs or HHCs. Carbon dioxide has been used for tertiary recovery of hydrocarbon resources. High levels of carbon recycle have been proposed to further recover such HeavyHCs. The cost of purchasing and delivering carbon dioxide, and the recycle costs are major costs for such CO2 enhanced HHC recovery.
The products of combustion, comprising steam or water vapor, and carbon dioxide, are commonly exhausted to the atmosphere when raising steam, resulting in loss of latent heat of combustion and carbon dioxide. Similarly the products of combustion (herein POC) from combustion power systems are commonly lost in recycling carbon dioxide for HHC recovery.
Some models and experiments suggest that vapor recovery hydrocarbon recovery rates may be about half that of Steam Assisted Gravity Drainage (herein SAGD) hydrocarbon recovery rates. Combining vapor recovery with SAGD may further enhance early HHC recovery. It can further enhance heat recovery from previous steam delivery.